Inside corner forms are used to form the inside corner of a concrete wall structure. Typically, the inside corner forms are used in the fabrication of tubular concrete structures, such as elevator shafts, stairwells, and box culverts.
To facilitate commercial usage inside corner forms must be easily assembled into place and easily removed from the casting. Further, all of the elements of the form should be interconnected to avoid the risk of losing parts between assemblies. Additionally, the inside corner form should be capable of closely aligning with the remaining portions of the form so that a smooth wall surface is created.
Inside corner forms are often fabricated to expand and contract into and out of the position for casting. This movement is ordinarily accomplished through the use of a screw or fluid operated actuating device. Examples of such forms are disclosed in U.S. Pat. No. 4,447,035 to Ivey et al., entitled "Joining Concrete Form Panels to Cast an Inside Corner Wall Structure" and U.S. Pat. No. 4,570,896 to Strickland et al., entitled "Slide Action Inside Corner Form." However, all such forms heretofore have lacked the desired structural integrity to ensure that the forming elements will be closely aligned with one another to avoid the forming of a rough and unsightly seam in the concrete structure. Further, grout (i.e., a cementitious runoff of excess water, cement, sand, etc.) seeping into and forming on the parts of the form has continued to be a persistent problem. This phenomenon causes the form to resist removal from the casting and requires significant cleaning of the form after each use. Moreover, screw operated forms require more time and effort to assemble and disassemble.